While the concept of implementing helicopter-like rotors on a winged aircraft can be traced back to as early as the 1930s, actual production of such aircraft took much longer to mature. The experimental Bell XV-3 aircraft, which was built in 1953, proved the fundamental soundness of the tiltrotor concept, and gathered data about technical improvements needed for future design.
A tiltrotor is an aircraft which utilizes one or more powered rotors (sometimes called proprotors) mounted on respective one or more tiltable structures. Those rotors may be used for both lift and propulsion, wherein different behavior is achieved when the rotors are tilted between a general vertical direction and a general horizontal direction, and in intermediate directions. Tilting of the rotors enables implementing, at certain times, vertical lift capability usually associated with helicopters, and at other times, the propeller propulsion usually associated with conventional fixed-wing aircraft. It is noted that while in tiltrotor aircraft usually only the rotor (and a structure onto which it is mounted) is usually tilted, tiltwing aircraft were also developed in which the entire wing—including the one or more rotors mounted thereon—is tilted.
Experiments in the field continued in the 1970's and 1980's with the development of the XV-15 twin-engine tiltrotor research aircraft, followed by the developing by Bell and Boeing Helicopters—starting in 1981—of the “V-22 Osprey” aircraft, which is a twin-turboshaft military tiltrotor aircraft for military needs. Another aircraft implementing tilt rotor technology is the commercial BA609 aircraft of Bell, teamed with AgustaWestland.
Tiltrotor unmanned aerial vehicles (UAVs) were also developed in the 1990's and 2000's, such as Bell's TR918 Eagle Eye, and IAI's Panther UAV.
By way of general background, the following publications disclose various aircraft configurations.
U.S. Pat. No. 7,267,300 discusses an aircraft comprising an airframe, a power plant mounted on the airframe, and at least two propellers rotatably mounted on the airframe and powered by the power plant for moving the aircraft in a generally forward direction during operation of the propellers. Also, the aircraft includes at least two counter-rotatable fan sets mounted on the airframe and powered by the power plant for providing upward lift to the aircraft during operation of the fan sets.
US 2006/0226281 discusses a vertical take-off and landing vehicle comprised of a fuselage having a front, a rear, and two lateral sides and a set of four thrusters set to the front, the left, the right, and the rear of said fuselage. The thrusters are comprised of a set of two counter rotating propellers both of which creates lift. The two counter rotating propellers cancel out the torque effect normally created by using only one propeller. The ducted fan units are movable between a first position in which they provide vertical lift and a second position in which they provide horizontal thrust using a set of servos and gears.
U.S. Pat. No. 7,472,863 discusses a vertical takeoff and landing (VTOL) aircraft design comprising one internal combustion engine able to spit shaft power to four fan units.
The fan units further employ counter rotating fan blades for stability. Separate horizontal and vertical tilting mechanisms delivered to the fan units are additionally disclosed. A variation in design is further included wherein electric motors provide the necessary shaft power.
US 2004/094662 discusses an Unusual Flying Object said to have VTOL capabilities including forward flight with a Linear Induction Magnetic Bearings power drive.
U.S. Pat. No. 7,461,811 discusses a STOL or VTOL winged aircraft comprising a fuselage and a fixed wing attached to the fuselage and extending outward from the two lateral sides thereof, forming one wing component extending outward from one side of the fuselage and a second wing component extending outward from the opposite side of the fuselage. At least one “thruster” is disposed in each wing component to provide vertical lift to the aircraft when the aircraft is stationary or moving forward only slowly. The thruster includes a shaft mounted for rotation in the respective wing component and extending substantially parallel to the wing axis and a plurality of fan blades attached to the shaft for movement of air.
US 2003/062442 discusses a personal aircraft said to be capable of vertical take-off and landing and comprises a passenger compartment having a front, a rear and two sides, and a plurality of independently powered thrusters attached to the outer periphery of the compartment. At least three thrusters are disposed on each side of the compartment. The thrusters, which are preferably ducted fan units, are capable of providing a vertically upward force to the compartment.
U.S. Pat. No. 6,892,979 discusses a personal aircraft said to be capable of vertical take-off and landing which comprises: (a) a fuselage having a front end, a rear end and two lateral sides, the fuselage having a central longitudinal axis extending from the front end to the rear end, between the two lateral sides; (b) at least one, and preferably two or more, ducted fans, each arranged in the fuselage between the front end and the rear end and between the two lateral sides, for providing vertical lift; and (c) at least one substantially horizontal wing attached to each side of the fuselage and extending outward with respect to the central longitudinal axis.
U.S. Pat. No. 6,464,166 discusses a vehicle, particularly a VTOL air vehicle, including a duct carried by the vehicle frame with the longitudinal axis of the duct perpendicular to the longitudinal axis of the vehicle frame; a propeller rotatably mounted within the duct about the longitudinal axis of the duct to force an ambient fluid, e.g. air, therethrough from its inlet at the upper end of the duct through its exit at the lower end of the duct, and thereby to produce an upward lift force applied to the vehicle; and a plurality of parallel, spaced vanes pivotally mounted to and across the inlet end of the duct about pivotal axes perpendicular to the longitudinal axis of the duct and substantially parallel to the longitudinal axis of the vehicle frame. The vanes are selectively pivotal to produce a set horizontal force component to the lift force applied to the vehicle. Various vane arrangements are disclosed for producing side, roll, pitch and yaw movements of the vehicle.
US 2003/080242 discusses an aircraft that is mounted with turbofan engines with separate core engines having fan engines used commonly for cruising and lifting up, through enabling to direct the thrust from fan engines to all directions by supporting the fan engines composing the turbofan engines with separate core engines in biaxial support so that the fan engines are rotatable in the direction of pitching and rolling, the fan engines are mounted on both sides of each of front and rear wings.
US 2007/0057113 discusses a system and method provided for a STOL/VTOL aircraft that stores required take-off power in the form of primarily an electric fan engine, and secondarily in the form of an internal combustion engine.
US 2008/0054121 discusses a VTOL vehicle comprising a fuselage having forward and aft propulsion units, each propulsion unit comprising a propeller located within an open-ended duct wall wherein a forward facing portion of the duct wall of at least the forward propulsion unit is comprised of at least one curved forward barrier mounted for horizontal sliding movement to open the forward facing portion to thereby permit air to flow into the forward facing portion when the VTOL vehicle is in forward flight.
US 2002/113165 discusses a vertical takeoff aircraft that uses ducted fans for lift and propulsion. The fans are attached to an airframe and are disposed on opposite lateral sides of the aircraft. The thrust from the each of the fans may be deflected in different directions by using vanes with flaps disposed within the ducts of the fans, as well as by tilting the entire fan assemblies.
U.S. Pat. No. 6,488,232 discusses a single passenger aircraft configured to vertically take-off and land. An airframe is configured to support the passenger in an upright position during take-off and landing and during flight. The aircraft includes a pair of propulsion devices that are mounted on an airframe above the level of the pilot. A set of hand operated control devices are mechanically linked to the propulsion devices for varying the orientation of the propulsion devices during flight.
WO 2010/137016 discusses a system and method for providing propulsion and control to an air vehicle, and for operating the vehicle, in which at least three propulsion units provide vertical thrust for vectored thrust flight, and in which at least one or two of the propulsion units also provide thrust for vectored thrust cruising or aerodynamic flight by suitably tilting the respective propulsion units for changing the thrust vector thereof. At the same time, the three or more propulsion units are operated to generate controlling moments to the air vehicle about three orthogonal axes, pitch, roll and yaw, during vectored thrust flight (hover, cruising, etc.) or during aerodynamic flight for controlling the vehicle. The control moments are generated by selectively varying the thrust generated by each of the propulsion units independently of one another, and: by selectively vectoring the thrust of one propulsion unit with respect to each of two independent tilt axes independently of one another, or by selectively vectoring the thrust of each of two propulsion units with respect to a respective tilt axis, independently of one another.
WO 2008/054234 discusses a propulsion system of a vertical takeoff and landing aircraft or vehicle moving in any fluid or vacuum and more particularly to a vector control system of the vehicle propulsion thrust allowing an independent displacement with six degrees of freedom, three degrees of translation in relation to its centre of mass and three degrees of rotation in relation to its centre of mass. The aircraft displacement ability using the propulsion system of the present invention depends on two main thrusters or propellers which can be tilted around pitch axis by means of tilting mechanisms, used to perform a forward or backward movement, can be tilted around roll axis by means of tilting mechanisms, used to perform lateral movements to the right or to the left and to perform upward or downward movements, the main thrusters being further used to perform rotations around the vehicle yaw axis and around the roll axis. The locomotion function also uses one or two auxiliary thrusters or propellers mainly used to control the rotation around the pitch axis, these thrusters or propellers and being fixed at or near the longitudinal axis of the vehicle, with their thrust perpendicular or nearly perpendicular to the roll and pitch axis of the vehicle.
Israeli patent application 217,501 discusses a control system configured to control a deceleration process of an air vehicle which comprises at least one tiltable propulsion unit, each of the at least one tiltable propulsion units is tiltable to provide a thrust whose direction is variable at least between a general vertical thrust vector direction and a general longitudinal thrust vector direction with respect to the air vehicle
There is a need in the art for an air vehicle that can descend to a hover and for systems, methods and computer program products for maneuvering of air vehicles, and especially of tilt-rotor air vehicles.